Ferromagnetic elements are used, for example, to form non-volatile memory cells. A plurality of such memory cells are interconnected by bitlines or sense lines and wordlines to create an array of storage elements for storing information. FIG. 1 shows a conventional ferromagnetic element 105. As shown, the magnetic element includes bottom and top magnetic layers 110 and 130. The magnetic layers, for example, comprise cobalt-iron or nickel-cobalt-iron. A non-magnetic layer 120 separates the first and second magnetic layers. The non-magnetic layer, for example, comprises an insulating material, such as aluminum oxide, to form a magnetic tunnel junction (MTJ) type element.
The magnetic element is typically rectangular or elliptical in shape, having a width and length L. The magnetic layers of the element are formed with an easy axis along the length L and a hard axis along the width. The magnetic vector 111 in the bottom layer is fixed or pinned in a first direction parallel to the easy axis. The bottom layer with the fixed magnetic vector is referred to as the reference or fixed layer. The magnetic vector 131 in the top magnetic layer can be switched between first and second (opposite) directions parallel to the easy axis. As such, the magnetic vectors in the layers can be oriented parallel or antiparallel to each other. The top magnetic layer with switchable magnetic vector is referred to as the storage or free layer.
The direction of the vectors in the top layer can be switched by the application of a magnetic field generated by passing a write current through, for example, the wordline. Depending on the magnetic field generated, the magnetic vector in the second layer either switches direction or remains the same. The magnetic element would have first and second resistance values based on whether the magnetic vectors are oriented parallel or anti-parallel, representing first and second logic states stored. For example, the magnetic element will have a high resistance value when the vectors of the layer are antiparallel to represent a logic 1 or a low resistance when the vectors are parallel to represent a logic 0. The states stored in the element can be read by passing a sense current through the element and sensing the difference between the resistances.
However, conventional magnetic elements require relatively large magnetic fields to switch the magnetic vector in the storage layer. In order to generate a sufficient magnetic field to switch the magnetic vector, a relatively high current is required. This results in a higher power consumption. Furthermore, larger switching currents are needed as cells size become smaller. The need for larger switching currents is undesirable, as this leads to a decrease in reliability, higher operating costs and in the case of mobile applications, shorter battery life.
From the foregoing discussion, it is desirable to provide a magnetic element which can switch with a low switching field.